1. Field of the Invention
The present invention relates to an apparatus and method for the enhanced removal of high viscosity crude oil from downhole formations.
2. Background of the Related Art
The quick and efficient movement of oil from its natural reservoir or formation, typically located thousands of feet below the earth""s surface, to the surface is important to the economically feasibility of producing from a given well. Increasing the temperature of oil that has a high viscosity will make the oil flow more efficiently and thereby possibly increase the amount of oil to be pumped while decreasing the operational expense of removing the oil.
The raising of the temperature of the oil located in the reservoir adjacent to the pump intake will increase the pump""s ability to quickly and more effectively move the oil from the reservoir to the production string. This will also increase the oil production rate for the well.
Another problem arises when oils contain a high percentage of paraffins. Paraffins will solidify as the temperature of the oil decreases. These paraffin deposits will form deposits, or a general coating, on the inside diameter of the tubular sections that are used to move the oil from the reservoir to the surface. It will also form deposits or a coating on the sucker rods that are used to pump the oil, if the well in question, uses this type of oil removal pumping devise. These deposits of paraffin restrict the flow of oil and will eventually choke off the flow of material to the surface. The resulting restricted flow not only reduces production rates but causes premature failure of the pump located in the oil reservoir and premature failure of the sucker rods in walking beam pumps and other type of pumps that are located whole in the reservoir area, an example of which would be a submersible pump. The result of this buildup causes a periodic shutdown of the well for various types of cleaning. Keeping these paraffins above the temperature where they solidify would prevent these deposits from occurring and thereby allow for longer production schedules.
Therefore, there is a need to raise the temperature of the oil while it is being transported from the reservoir to the surface. Since oil is made up hydrocarbons and is therefore combustible, it is desirable that a method be devised to raise the temperature without the use of heating devises that are placed down hole where exposure to these high temperature devises may cause ignition of these hydrocarbons. Additionally, the use of other methods of warming the oil, such as using other precious resources like water, are considered to be inappropriate since there is a danger that the water would become contaminated by oil, or other chemical components located below the earth""s surface. It is also important that a method be provided that supplies a consistent source of warmth to provide consistent production without interruptions.
The present invention provides a method of increasing oil production from a downhole formation through a production tubing to a wellhead. One embodiment of the method comprises heating a working fluid at the wellhead and circulating the heated working fluid through a conduit that is secured in thermal communication with the production tubing. The conduit extends from a heating system adjacent the wellhead to a downhole pump at a distal end of the production tubing and back to the heating system. Preferably, the rate of heat transfer from the working fluid to the oil in the production tubing is controlled to increase the rate of oil production. The step of controlling the rate of heat transfer may include a step selected from controlling the temperature of the working fluid exiting the heating system, controlling the rate of circulating the working fluid, or a combination thereof. It is preferred that the conduit allow for the expansion of the working fluid. It is also preferred to monitor the temperature of the oil produced from the production tubing at the wellhead and monitor the flow rate of the oil produced from the production tubing at the wellhead. The method provides the ability to control the working fluid temperature exiting the heating system to produce a desired flow rate of the oil.
The invention also provides a system or apparatus for increasing oil production from a downhole formation through a production tubing to a wellhead. The system comprises a heater adjacent the wellhead for heating a working fluid, a pump adjacent the wellhead for circulating the working fluid, and a closed loop of tubing filled with the working fluid. The closed loop of tubing includes the heater and the pump, and the closed loop of tubing is secured in thermal communication with the production tubing. A plurality of clamps are used to secure the closed loop of tubing in thermal communication with the production tubing, wherein the clamps are spaced apart along the production tubing down to the distal end of the production tubing. The preferred embodiment further comprises an accumulator in fluid communication with the close loop to allow expansion of the working fluid. The system is preferably controlled by a programmable controller in electronic communication with a flow meter for measuring the rate of oil production through the production tubing, a temperature probe for measuring the temperature of the oil, and/or a temperature probe for measuring the temperature of the working fluid. Optionally, the controller may be programmed to increase the temperature of the working fluid exiting the heater in order to provide an increase in the rate of oil production. It is also optional for the pump to include a variable speed motor allowing for changes in the circulation rate of the working fluid. Finally, the closed loop may also include one or more devices selected from an air purge line, a pressure sensor, or combinations thereof.